Studies were conducted to examine the specificity of the effects produced by amplifier T cells and suppressor T cells involved in the antibody response to Type III pneumococcal polysaccharide (SSS-III). The results obtained showed that (a) amplifier T cells generated after immunization with SSS-III influence only those antibody-forming cells stimulated by SSS-III, and that (b) the effects produced by suppressor T cells were antigen-specific with regard to both their induction and expression. The role of the idiotypic determinant of cell-associated antibody specific for SSS-III in the generation of these types of regulatory T cell activities is being assessed.